That's the conventional wisdom (and to be fair 99% likely) but I'm sticking with Georgy throwing a curveball.Ned's sister Lyanna's kid is Jon Snow, but the father is Rhaegar Targaryen, eldest son of King Aerys Targaryen, who'd be next in line for the iron throne making his son next in line after his death (which - surprise surprise - happened).
Ned claimed the baby as his after his sister died in childbirth (that was the scream Ned heard), in order to protect it after Jamie Lannister killed Aerys and the lannisters took king's landing and proceeded to kill the rest of the "mad King"'s family to end his line.
This also makes daenerys his cousin and the former nights watch maester (Aerys' brother? Other son?) Jon Snow's ... uncle?